I was late to this party.
News about the leak of Google’s internal Search API documentation was doing the rounds back in May 2024… and slid right past me, undetected.
So, to those who follow SEO closely, this will be old news – but for anyone who, like me, missed that memo, it’s worth a closer look.
The documentation revealed thousands of internal attributes relating to the way Google analyses, stores, and ranks content.
And buried within that mountain of signals were two that caused a particular stir:
siteFocusScore and siteRadius.
• siteFocusScore: an indicator of how ‘thematically concentrated’ a website is.
• siteRadius: a measure of how far individual pages stray from that central thematic core.
Together, they paint a picture of Google evaluating not just page-level relevance, but the coherence of an entire site’s topical identity.
This is all firmly in SEO territory, but there’s a good reason for PPC practitioners to pay attention.
Google doesn’t maintain two completely separate systems for understanding webpages in organic vs. paid search… The same crawlers fetch them; the same parsing systems structure them, and the same semantic models interpret meaning.
Google has increasingly talked about applying shared AI and understanding capabilities across its products, and historically, we’ve seen that changes to search indexing priorities (e.g. mobile friendliness / Core Web Vitals) tend to surface in Ads’ landing page assessments soon after.
Landing Page Experience (estimated to be around 39% of Quality score) feeds indirectly into Ad Rank. It’s rarely the main lever we look to pull, but it’s one factor we can (sometimes) control that sits outside of our Google Ads accounts, and truly influences the auction.
So it’s worth entertaining the possibility that these signals relating to ‘topical coherence’ may influence how landing pages are interpreted for ads too.
That doesn’t mean Google necessarily penalises advertisers for publishing broader content, but it does suggest that landing pages may work better when they belong to a site whose overall content aligns naturally with the advertised topic.
Pages that sit on sites with very disparate or inconsistent themes may be evaluated less favourably compared to those on tightly focused sites.
If Google is indeed modelling – and valuing – topical coherence across domains, advertisers should take note.
You don’t need to redesign a site to please an algorithm, but it’s worth taking stock of where you stand. Here are a few simple ways to assess your site’s topical coherence:
1. Look at your site from a distance. If someone landed on your homepage, could they quickly describe what your business is about in one sentence? If the answer isn’t immediately clear, that’s your first signal.
2. Review your main navigation and content categories. Do they cluster around related themes, or do they jump between unrelated topics? A site selling industrial equipment that also has extensive sections on lifestyle tips and travel photography is sending mixed signals.
3. Audit your page titles and headings. Use a tool like Screaming Frog or just review your sitemap. Do your pages tell a coherent story about your offering, or are they scattered across unconnected subjects?
4. Consider your blog content. Does it reinforce your core offering or range into tangential topics? Broader content serves a purpose, but it’s worth recognising that it may be diluting your site’s thematic focus.
Many successful advertisers operate on broad marketplace sites or lead-gen aggregators, but for owned sites where you control the content strategy, thematic coherence is worth keeping on your radar.
When Google is confident that your site is firmly rooted in the topic you’re advertising, that confidence likely flows through to your Landing Page Experience score, your Quality Score, and ultimately your required bids.
